By determining the amino acid changes generated in Drosophila alcohol dehydrogenase by various mutagens, we hope to deduce the molecular mechanisms of the mutagenic event. Drosophila alcohol dehydrogenase is an ideal enzyme for this purpose because it makes up a large proportion of the soluble protein of the adult fly, is readily purifiable by both traditional means and by antibody precipitation, and because mutants that affect the enzyme are easily detected and isolated.